The present invention relates to pumps in general, and more particularly to plunger-type pumps.
Pumps of different constructions and working accoding to different principles, have already been developed and are in widespread use. Their constructions will vary in accordance with the requirements which such pumps have to satisfy, such as the properties of the medium to be pumped, the volume to be pumped by the pump in time unit, whether the pumping action must be continuous or may be intermittent, and the pressure differential to be generated by the pump, to name just a few.
There has also been proposed a plunger-type pump in which a pump housing defines a pumping chamber, and an elongated plunger is accommodated in the pumping chamber and reciprocates in the pump housing. The introduction of the medium to be pumped into, and discharge of such medium from, the pumping chamber is controlled by valves both at the inlet side and on the outlet side of the pump. A particularly simple construction and a reliable operation of this type of pump are obtained when the inlet-side valve is constructed as a sleeve valve mounted on and surrounding the plunger. The sleeve valve, to a limited extent, is entrained by the plunger for joint reciprocation therewith, against a force of a biasing spring acting upon the sleeve valve and urging the same toward a closing position thereof. In the latter position, the sleeve valve subdivides the pumping chamber into a suction space containing low-pressure medium and surrounding the sleeve valve, being in communication with the inlet port, and a pressure space in which the medium is pressurized during the pumping stroke of the plunger and from which it is discharged into the outlet port upon the opening of the one-way valve at the outlet side of the pump.
While this particular type of a pump has many advantages, it is also possessed of several drawbacks. Fist of all, such a pump can be used for pumping only certain media, particularly such which are not overly toxic, noxious or aggressive, while it is not suited for pumping media which tend to form deposits or encrustations at relatively calm regions of the pump, which tend to attack and corrode or erode the materials of the various components of the pump, or which could create a hazardous condition if permitted to escape from the pump to the exterior thereof. Another disadvantage of a pump of this construction is that it is very difficult, if not impossible, to achieve hermetic sealing of the pump, and that the seals employed heretofore were, for this rason, necessarily very complex, and therefore expensive.